MX (Mail Exchange) records are DNS records that are used to specify the servers responsible for handling email messages for a domain. They are used to route email to the correct mail server for a domain.
An MX record consists of two parts: a domain name and a priority value. The domain name specifies the server that is responsible for handling email for the domain, and the priority value determines the order in which the server should be tried if it is unavailable.
For example, consider a domain called "example.com" that has two MX records:
MX 10 mail.example.com
MX 20 backup.example.com
In this case, email for the domain "example.com" should be sent to the server "mail.example.com" first. If that server is unavailable, the email should be sent to "backup.example.com". The priority value of "10" for "mail.example.com" indicates that it should be tried first, while the priority value of "20" for "backup.example.com" indicates that it should be tried second.
MX records are used by email servers to determine the correct route for delivering email to a particular domain. They are an important part of the infrastructure that enables email to be sent and received on the internet.